Line a large baking sheet with parchment paper and set it aside. This will give the coated cereal plenty of room to cool without sticking together.
Place the butterscotch chips in a microwave-safe bowl. Microwave at 50% power in 30-second intervals, stirring after each interval, until the chips are mostly melted and smooth. This usually takes around 1–2 minutes, depending on your microwave.
Place the Rice Chex cereal in a medium mixing bowl. Pour the melted butterscotch over the cereal and gently fold with a spatula until the pieces are lightly coated. Work carefully to avoid crushing the cereal.
Spread the coated cereal in a single layer on the prepared baking sheet. Allow it to cool for about 10–15 minutes, or until the butterscotch coating has hardened.
In a large bowl, combine the mini pretzels, Reese’s Pieces, candy corn, chocolate-covered pretzels, and salted peanuts or caramel corn if using. Toss gently to distribute the ingredients evenly.
Break apart any large clusters of butterscotch-coated cereal and add them to the bowl. Gently toss everything together until the candy, pretzels, and cereal are evenly mixed.
Transfer the Halloween Snack Mix to a large serving bowl or divide it into individual treat bags. Serve immediately, or store it in an airtight container in a cool, dry place to keep it crunchy.
